This invention relates to a spark plug for internal combustion engines for preventing quench operation of a flame nuclei due to a center electrode and an outer or ground electrode, thereby improving ignitability thereof.
There have been provided many methods for producing the quench operation of the flame nuclei due to a center electrode and an outer electrode, particularly for preventing misfires under an engine running condition in which the ignitability is low, such as during idle speed.
Within the prior art many such spark plug designs having various projections and surfaces are known. Typical are the annular surfaces shown in the inner and outer electrodes surfaces of U.S. Pat. No. 4,015,160, the annular ring and channel arrangement of U.S. Pat. No. 4,023,058 and the V-type ground electrode with a channel shown in U.S. Pat. No. 2,226,415. Additional prior art is shown in U.S. Pat. No. 3,970,885 which includes, in addition to various groove embodiments a projection provided on the ground electrode (element 36, FIG. 25). As set forth in that patent, the projection is disposed in the spark discharge area confronting the tip surface of the center electrode. The flame nuclei produced by the spark are rapidly spread out over the projection to facilitate growth of flame nuclei and easy propagation of flame. The hallmark of all these prior art devices is the modification of the ground electrode to limit the area of the grounded surface. However, it has been found that many deficiencies remain, in actual use, so these spark plugs do not satisfactorily perform, especially in an idle speed engine condition.
One method shown in my co-pending application is that an end portion of the center electrode is tapered or that a groove is formed in the end surface of the center electrode or the outer electrode surface confronting the center electrode. However, according to the above-described methods it is impossible to obtain a sufficient improvement of ignitability.